Preheat panini grill to high heat. In a large skillet over medium-high heat, melt the butter and add 3 Tbsp. olive oil. Wen hot, add 4 cloves minced garlic and bella and shitake mushrooms. Saute for 3 minutes, then add thyme, pepper, salt and balsamic vinegar and cook for 3 additional minutes or until mushrooms are tender but not soft. Remove from heat and set aside.

Combine remaining minced garlic with remaining olive oil in a small bowl. Brush one side of 8 slices of bread with olive oil/garlic mixture. Spread mascarpone cheese evenly on the inside of 8 slices of bread, then top with 4 slices fontina cheese. Place fontina topped slices oiled side down on panini grill, then top with remaining slices of bread, oiled side up. Close panini grill and cook until golden brown and the cheese is melted, about 10 minutes. Remove from grill and pull sandwiches apart, leaving cheese on both sides. Lay out on serving dish and top each with mushrooms mixture. Garnish with more fresh thyme. Serve warm.

*Note-- sometimes I use a mixture of 3-4 kinds of mushrooms.